This invention relates to opto-isolators with enhanced optical coupling, and a method of manufacturing, such devices.
Optical coupling devices, known in the art as "opto-isolators" are used in a variety of circuit applications where it is desired to electrically isolate input and output circuits. For example, such devices may be used as switches and for transmitting analog signals.
The opto-isolator basically comprises a light-emitting element, such as a GaP light-emitting diode, in combination with a poto-detector such as a silicon diode, transistor, or darlington pair. The prior art method of fabrication usually involves forming the light-emitting diode and detector as discrete elements, bonding the elements to separate lead frames, and then positioning the lead frames so that the elements are in close proximity. The elements are then encapsulated, and the lead frames cut apart to form discrete four lead devices (see, for example, U.S. Pat. No. 3,660,669 issued to Grenon). This is, in general, a satisfactory method of manufacture. However, it is desirable in mass production to provide for a more efficient means of assembling the devices. Further, in such prior art devices, the light-emitting element and photodetector are placed face-to-face or side-to-side, and since the GaP device emits light from all surfaces, such a structure does not utilize all of the light emitted. Thus, it is also desirable to provide a structure with enhanced optical coupling between light emitter and detector.